There exists a well-known principle by which water or any liquid can be metered in a controlled fashion into a container or into the ground. This is called the "Marriotte" principle and is utilized in British Patent No. 874,729, issued Aug. 10, 1961 to R. C. Bracey. In FIG. 2 of the said patent there is shown a simplified "Marriotte" construction in which a plant receptacle is adjacent a water compartment that is sealed at the top and has an opening toward the bottom communicating with the receptacle. A tube provides communication between the atmosphere and a location in the compartment which is below the level of water in the compartment. This means that, within the compartment, the level of atmospheric pressure is at the bottom of the tube, and the water above this level is at a pressure below atmospheric. In this prior art patent, the opening into the plant receptacle is approximately at the same horizontal level as the bottom of the tube. As water passes out of the compartment through the opening and into the plant receptacle, air enters from the atmosphere through the tube to replace the removed water. In effect, this principle provides a constant-level "water table" within the plant receptacle.
Other prior art patents of interest are U.K. Patent No. 14,554, issued Dec. 12, 1907 to Gelezius; Canadian Patent No. 951,516, issued July 23, 1974 to Crane; and Canadian Patent No. 961,641, issued Jan. 28, 1975 to Crane.
While the Marriotte system shown in British Patent No. 874,729 provides in many cases a satisfactory watering system for plants, there are numerous instances in which the establishment of the top of an effective water table within a plant receptacle, whether constant or not, does not represent an ideal situation. In fact, most plants, miniature trees, etc. in nature do not grow in conditions where the water table is found only a few inches below the surface of the ground. For many species, such conditions represent over-watering and could lead to poor growth or the death of the plant.
A far more realistic condition is one in which the top of the effective water table is located some distance below the roots of the plant, in order to avoid over-watering. However, with the ordinary Marriotte system, this can be accomplished only by increasing the vertical depth of the receptacle, and ensuring that the bottom of the air-admitting tube in the water compartment is located adjacent the very bottom of the deep receptacle. Clearly, this is not a practical solution to the problem.